Evolution Exam 4

Natural selection

heritable variation in population and non-random survival and reproduction
consistent differences in fitness among individuals

lifetime reproductive fitness (R)

the extent to which an individual contributes genes to the next generation
individual fitness

Relative fitness (W)

0 to 1
relative to a reference genotype (typically fittest with highest R)
W = 1 for fittest
W < 1 for others

Selection coefficient (S)

amount by which a genotype's relative fitness differs from the fittest genotype
S = 1 - W
S = 0 = fittest
S = 1 = no fitness

directional selection

example:
AA increases
AB no change
BB decreases
= shift to the left

heterozygote advantage/balancing selection

example:
AA and BB decrease
AB increases

heterozygote disadvantage

example:
AB decreases
AA and BB increases

Directional with multiple loci

change in population mean value, decreased variation, increase in mean, curve gets narrower

Stabilizing

no change in mean, reduced variation, selection against extremes

Disruptive

no change in mean, increased variance, move towards the extremes

frequency-dependent selection

the fitness of a genotype depends on its frequency

positive frequency-dependent selection

the more common a genotype is, the higher its fitness
ex. butterfly color morphs (safety in numbers)

Inverse (negative) frequency-dependent selection

the less common a genotype is the higher its fitness
ex. salamander polymorph for the presence of stripes (goes back and forth for stripes being beneficial or harmful)

dominant beneficial alleles

always causes fast evolution at first, then much slower as it approaches fixation

recessive beneficial alleles

depends on initial frequency of allele
if uncommon, the very slow at start
if common, then selection is very fast and efficient

recessive deleterious alleles

able to hide in heterozygotes causing them to be "invisible" to natural selection leaving them to be persist at low frequencies

mutation-selection balance

conditions under which the mutation rate at a give locus = the strength of selection against deleterious alleles at that locus

gene flow and natural selection

gene flow disrupts natural adaptation
high gene flow can lead to maladaption

genetic drift and natural selection

genetic drift can override selection in some cases
when genetic drift is stronger, alleles are lost or fixed regardless of their effect on fitness

costs to sex

meiosis (sexual) takes longer than mitosis (asexual)
breaks up adaptive combinations of alleles at multilocus geneotypes
time/energy spent competing for and looking for mates
increased risk of predation and disease
males don't do shit for the population

benefits of sex

better at combining beneficial mutations in one genome
purging deleterious mutations (parents can produce offspring that have higher fitness than themselves)
contributes to variation (speeds up adaptation)
response to changing environment
recombination/breaking linkage disequilibrium
allows populations to stay one step ahead of their parasites

Muller's ratchet and genetic load

asexual genome cannot produce offspring better than itself but it can produce worse
number of mutations carried by a genotype accumulates over time

mutational meltdown

too many bad mutations that accumulate in genome leading to the population dying off

antagonistic coevolution

host vs parasite/pathogen, perpetual cycle leads to a need for continual innovation

Red Queen hypothesis

sexual reproduction generates variation quickly, which ensures that some individuals will be resistant to parasites
target of selection is constantly shifting as parasites evolve as well

secondary sexual characteristics

any phenotype involved in attracting a mate that is not directly necessary for sexual reproduction
often detrimental to survival
do not appear until adulthood

sexual selection

differential reproduction due to variation in the ability to obtain mates

sperm

small, motile, energetically inexpensive, produced in large quantities

egg

large, sessile, energetically expensive, produced in small quantities

Bateman gradient

male reproductive success improves with additional matings
female reproductive success less affect by additional matings

males

nearly infinite reproductive potential
limited by ability to attract, inseminate, or monopolize females
increase reproductive output = high variance in male reproductive success

females

finite reproductive potential
limited by times and resources available to invest in each offspring
need only mate once to achieve maximum reproduce success = low variance in female reproductive success

intrasexual

competition between males for access to females

intersexual

females choice of courting males

contest competition

males fighting over females/territory

Scramble competition

everyone comes together for a short time, woever gets to the female first wins

parental males

build nest, guard eggs, court females

female mimics

pretend to be interested in mating then release sperm

sneakers

small and release sperm when nobodies looking

post-copulatory sexual selection

competition between males continues after mating has taken place

sexual conflict

interests of males and females do not align

choice based on resources

direct benefits
superior territories or nuptial gifts

sexy sons

genetic correlation between female preference and male traits

genetic benefits

preferred traits are "honest signal" of genetic quality

trade offs

allocation to one fitness component reduces the resources available to other fitness components

Senescence

late-life decline in an individual's fertility and probability of survival
caused by: failure to repair damage in genome; errors in replication, transcription, translation, and accumulation of toxic metabolic by-products

mutation accumulation theory

mutations causing senescence are only weakly selected against
by the time some mutations appear, the individual has already reproduced meaning those mutations are not eliminated by natural selection

antagonistic pleiotropy hypothesis

mutations that provide early reproduction benefit will be favored by selection even at a later cost
there is always a chance of dying so reproducing early has a higher benefit
genes that favor early reproduction also spread more quickly because they reproduce more often

Absolute fitness (R)

incorporates both survival and reproductive success
R is sum of expected survival and reproduction per unit of time (x) over the lifespan
R = (lx)(mx)

Grandmother hypothesis

menopause is a life-history adaptation associated with increased survival to help feed/care for grandchildren
better to invest in grandchildren

Semelparous

reproduce in one big bout then die

Semelparous favored when:

big individuals produce exponentially more offspring than small individuals
probability of survival increases with body size (store up resources to reproduce)
risk: die before able to reproduce

Iteroparous

reproduce throughout life

Iteroparous is favored when...

adults have high survival from one year to the next
environment unstable (choose not to have offspring)

sequential hermaphrodites

change sex once they reach a certain body size
favored if small individuals have higher fitness as one sex and large individuals are have higher fitness as the opposite sex

Protandry

start as male and transition to female
ex. small male cannot mate due to larger male so they change to female so they can at least reproduce

Protogyny

Start as female and transition to male
ex. if largest male dies then the largest female can change to be male to hold the territory

Optimal clutch size

selection will favor clutch size that produces the most surviving offspring
equilibrium point at which clutch size/probability of survival is maximized